Double seat block and bleed valves are in wide use in industry, for example in the food, dairy, beverage, pharmaceutical and biotechnology businesses. One example of such a double seat valve is a valve that is operated in connection with two flow conduit paths. In some applications, such as for example the industries mentioned above, it is desirable sometimes to interrupt the flow of the material and instead flush the system using a clean-in-place solution. One way this is sometimes accomplished is that the process material continues to flow through one conduit, while the clean-in-place solution flows through the other conduit.
In such systems, it is desirable that the process material be very well sealed and segregated from the clean-in-place solution so that the process material and the clean-in-place solution do not contact one another. In one example of such type of system, each conduit has a respective seat, and each conduit has a respective closing member or stem (usually as a reciprocating flanged valve stem), and the closing members can each be axially moved between a position sealing the seat and a position opening the seat. In the cleaning position, a valve associated with a respective conduit is opened when cleaning solution is in the conduit, and the cleaning solution is thus permitted to move from the conduit and exit through a drain. This cleaning process can occur while the other valve is closed, and process material is flowing through the other conduit.
A potential aspect of an arrangement having two seats and two closing members, is that when one of the valve seats is open (for example during a cleaning flush) there is only a single seal (typically an O-ring seal) that exists between the cleaning solution and the material. This seal may sometimes be subject to impingement of cleaning solution which is under a high velocity, particularly in designs where the cleaning valve is only opened by a small gap, and the clean-in-place solution squirts through the open gap at high velocity. It would be desirable in some applications and circumstances to avoid the effect of this impingement, at least to some extent.